Figure 2: Optimal concentration of oligonucleotide for immobilization on aldehyde surface. The oligonucleotides were dissolved in different concentrations in spotting solutions and hybridized to random-labeled oligomers. The signal intensity is deduced from processed slides and there is no signifi cant difference in signal intensity from 40 to 100 ýM concentration gradients implying that 40 mM is the minimum required concentration of the oligonucleotide for spotted microarrays